Selection of bacterial mutants from Salmonella specifically recognizing determinants on the cell surface of activated T lymphocytes. A novel system to define cell surface structures.

The isolation of bacterial mutants from Salmonella is described with specific binding capacities to allogeneically or concanavalin A-activated T lymphocytes. The enrichment of these mutants was achieved by separation of T cell blasts with adhering mutants from nonresponsive lymphocytes and nonadhering bacteria through 1 x g sedimentation. Binding of the mutants was specific for T cells early after antigen or mitogen stimulation. No adherence was observed with unstimulated T or B lymphocytes and with B cell blasts. Further results suggested that the binding of Salmonella mutants was mediated by the heteropolysaccharide moiety of lipopolysaccharides with a specificity for protein receptor sites on activated T lymphocytes. Significantly, these heteropolysaccharides also inhibited the differentiation of prekiller to killer cells from allogeneic mixed lymphocyte cultures but did not depress the proliferative response or the activity of cytotoxic effector cells. Bacterial adherence, as well as polysaccharide activity in functional tests, showed strain specificity since reactivity could only be obtained with activated T cells from AKR, C57BL/6, C3H but not with BALB/c and A/J strain mice. It is discussed whether the heteropolysaccharides mimic the structure of naturally occurring molecules and thus compete for their receptor sites. Selection of bacterial mutants with adherence properties may become a general procedure for detecting cell surface molecules on lymphoid and nonlymphoid cells.